With the continuing need of pursuing performance improvement in electronic products, such as computer, communications and handheld devices, and in order to cope with the tendency of miniaturization, high-speed and high-capacity in microelectronics products, the interconnects between transistor devices and wafer carrier board are designed to continuously shrink. When the wire size is less than 500 nm, the current density will be as high as 106 Amp/cm2.
In order to cope with the tendency of miniaturization, high-speed and high-capacity in microelectronics products, the interconnection between transistor devices and wafer carrier board is designed to continuously shrink, resulting in a dramatic increase in the current density of the wire (>105 Amp/cm2). However, the high-density current passing through the wire may cause void or hillock generated therebetween, which is analogous to the electromigration phenomenon occurred in the wires that causes short circuit or open circuit and so on. Therefore, the reliability of the wire becomes an important issue. Copper alloy wire is considered to be a potential solution that may solve electromigration of the electronic wire. According to the guidelines for wire selection specified in ITRS (international technology roadmap for semiconductor) in 2007, the specific resistance value is an important indicator, which must be less than 2.2 μΩcm. Compared with the specific resistance value of the wire plated with copper, which is 1.7˜1.9 μΩcm, it is necessary to consider the difference between the specific resistance values in selecting copper alloy wire. Because silver has excellent conductive properties, the copper-silver alloy wire is considered to be a potentially appropriate improvement candidate. The copper-silver alloy film has a specific resistance value of about 2.0˜3.0 μΩcm, depending on the silver content and the deposition method. Compared with copper metal, the copper-silver alloy has improved mechanical strength and electromigration resistance.
Regarding the researches in copper-silver metal plating solution system and its copper-silver plating layer, the acid formulation plating system using copper silver sulfate, published by S. Strehle et. al. (Thin Solid Film, 519, 3522 (2011)  Thin Solid Films, 517.11, 3320 (2009)  Microelectronic Engineering, 87.2, 180 (2010)), is the first study discussing the effect of copper-silver metal plating in the electromigration aspects of electronic wires. In the foresaid study, the plating solution composed of the aqueous solution of copper sulfate, silver nitrate, and sulfuric acid was used, and the concentration of added silver nitrate (1.5×10−4˜3×10−3 M) and the current density (0.5˜3 ASD) were adjusted to control the silver content of the plating layer. Regarding the finished copper-silver plating layer, the thickness was 1 μm and the silver content of the plating layer can be controlled at 0˜4 at. %. M. J. Kim et al. employed alkaline cyanide plating solution to carry out the copper-silver metal plating (J. Electrochem. Soc., 159, D253 (2012)), which mainly perform LSV analysis and the development of copper-silver metal plating processes. In addition, Bernasconi et al. published a copper/silver pyrophosphate plating solution (ECS Transactions, 58.32, 53 (2014)), which mainly controlled the silver content of the plating layer by a process current density of 2 to 5 mA/cm2, resulting in silver content of the plating layer between 3-16 at. %. As the current density increased, the silver content of the plating layer decreased. U.S. Pat. No. 7,821,135 used an alkaline plating solution system of pyrophosphoric acid or ethylenediamine. However, the above study didn't mention how the acidic solution in the electroplating process avoids AgCl precipitation to affect the effect of electroplating. In addition, in consideration of the toxic characteristics of the plating solutions, such as copper sulfate and cyanide, and the condition of using photoresist in the wire definition process, it is not easy to proceed with the industrial applications.
Therefore, there exists a need for an innovative copper-silver dual-component metal electroplating solution and electroplating method in the industry. The electroplating solution has environmental protection characteristics, such as less poisoning hazards, and can avoid the precipitation phenomenon that may exist during the plating process in order to prepare the copper-silver dual-component metal material that meets the need of the industry.